angular2

This article is all about my experiences of building a Native Android application using NativeScript. NativeScript a framework for building cross-platform Android & iOS apps using Javascript and XML. For the reference, I am in the middle of migrating the same application to NativeScript + Angular combo (just for fun) as it leverages existing Angular skillset such as data-binding, event handling, routing, AuthGuard, etc, and makes it easy to reason about as well.

In a nutshell, NativeScript is not just a set of Javascript libraries but more of a runtime that enables to call Native Android and iOS apis using Javascript. It uses a Javascript virtual machine – V8 for Android and Webkit Core for iOS – that interprets and executes Javascript code at runtime to their respective native code. Hence, there is no limit in terms of which native API can be called in NativeScript, makes it a super powerful tool – worth adding in your arsenal 🙂

This article does not discuss about building Native apps in NativeScript because their documentation is pretty neat and covers it all.

Android ecosystem

Even though you were convinced to write native apps in pure Javascript, that fact is partially true. Meaning you still need to setup android SDK and tools in order to run your application on Emulator or Device. Oh boy, it was PITA in the beginning, especially when you are used to write for Web only – just Write. Refresh. Repeat!

One of such issues faced even before I could run their Sample Groceries app was the ANDROID_HOME environment variable is not set error, while running tns platform add android command. Although, there were tons of stack-overflow answers about that weirdo behavior but unfortunately all were suggesting to add ANDROID_HOME to the PATH environment variable – been there, done that already. At one point, I had decided to give up on NativeScript as I was this frustrated!

But soon the NativeScript community slack channel came to the rescue which I found on their troubleshooting documentation. That culprit is sudo – was running sudo tns platform add android like a rookie 👊. Nonetheless, I quickly got over it and set up the project with tns create FreshCall command.

NativeScript Plugins

The android application named FreshCall that I was building is a simple phone call management app to keep a tap on number of users being called on a daily/weekly basis, extract call charges for reimbursement purposes, and possibly record a phone conversation (with speakers on) for quality purposes. As you have already guessed that the application supposed to use android native APIs for most of the requirements such as ask permissions, choose or dial contact numbers, record conversation and upload it to Firebase, fetch call charges from USSD dialogs, etc. Luckily, the NativeScript community is flourished enough to have many plugins ready for most of the things I needed 😊

I realized that building traditional apps in NativeScript is far more easier than ones using native APIs. That’s why problems and worries did not stop for me at the rookie mistake made earlier, after all it was just the beginning.

Migrate Android code to NativeScript

Obvious thing for any phone management application is to detect Incoming calls and allow to make Outgoing calls using TelephonyManager. Truck load of articles and stack-overflow questions can be found on the topic, however, using them in NativeScript was a big deal. But Extending native classes section from the NativeScript documentation was quite useful that opened up ways for further exploration.

Background Services

NativeScript community is so kind to give you all the tools to build a bridge, but the only condition is that you’ve to learn to build it yourself, 😄. I hope one day it will be a piece of cake as NativeScript grows and will be widely adopted as a standard to build native apps.

To track the USSD dialog’s response – the call charge window appears after the call ends – I needed a background service to keep an eye on it and extract the the call charge as soon as it shows up. Somehow I could write a background service myself with the help of the sample provided by NativeScript community and port the USSD parsing using the trick we just learned. However, the onServiceConnected() method – enables accessibility service to read USSD responses – was not getting registered even after enabling it for the application from the android settings.

During the salvation of this problem, I learned two things:

When in doubt, always rebuild using tns build android (remove the existing application from the device before live-syncing again).

Reinstall android packages if updates are available.Android SDK and tools

Wrap up

Experience of building the android application (without having any knowledge of Native Application Development before) was terribly empowering 😉. My advice to fellow developers is to keep Android Documentation open all the time!

Peter Kanev from NativeScript core team had been a great help. Also, special thanks to Brad Martin (who built many plugins I’ve been using) and Marek Maszay for their constant support and cheer on Slack.

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In the previous article, we had explored how dependency injection works in Angular2 compared to Angular1. In this article, I will walk you through the one-way vs two way data binding and how its different but quite similar in Angular2.

Angular1

As usual, we’ll quickly go through the Angular1 example. Let’s take a simple example (HTML) from my free ebook on Angular1 Directives that explores how data binding works in Angular1. Notice we have not written a single line of Javascript code to enable the data binding in the following example:

We are already familiar with Component, ES6 Class, bootstrap, etc. jargons from the first article as those are the backbone of Angular2. The only difference here is the template with data-binding expressions.

In Angular1, the two-way data binding was enabled by default, for one-way data binding the expression should be wrapped in {{choose}}. Also the attribute name supposed to be hyphenated. However, in Angular2 the attribute should be in camel-case with subtle differences that affect the way data flows:

[Component -> Template]To show a model in a template which was defined in the component, use square-bracket or double-curly syntax a.k.a. One Way Binding.

(Template -> Component)To broadcast an event from a template in order to update the model in the component, use round-bracket syntax a.k.a. One Way Binding.

This clearly means that the two-way binding in Angular2 is opt-in and can be enabled by importing BrowserModule to plug it in the NgModule.

In the above example, we want to toggle the expression choose from the template to the component using (click) when the button is clicked and update the checkbox in the template immediately using [ngModel]="choose". We also want to update the model choose in the component if the checkbox is toggled manually using [(ngModel)]="choose". Do not get confused with one-time binding in Angular1 i.e. {{::choose}} where the model used to be freezed once evaluated, there is no such thing in Angular2.

In the last article, we’ve explored basic differences between Angular 1 and 2 with respect to Component over Directive, TypeScript over ES5, ES6 Class over Controller, and Decorators/Annotations. We’ve pretty much got acquainted with setting up Angular2 in TypeScript with SystemJS to begin our journey with Angular2 in coming weeks. In this article, we’ll investigate how dependency injection that we always loved is different in Angular2 than Angular1. We are not going to cover what dependency injection is in this article though, so if you are not familiar with it yet, follow the documentation for more information.

Angular1

As usual, we’ll quickly go through the Angular1 example. Let’s take a simple example (HTML and JS) from my free ebook on Angular1 Directives that explores how DI works in Angular1. Notice we’ve used ngController directive in which we are going to inject a custom service. Also stare at ngApp directive which was a recommended way to bootstrap an application automatically in Angular1 rather than manually using angular.bootstrap method.

We are already familiar with Component, ES6 Class, bootstrap, etc. jargons from the previous article as these are the backbone of Angular2. The only difference here is the service, HelloService. However, if you notice, the service is itself a ES6 Class similar to our application component, DI. Just like @Component annotation is there to tell Angular2 to treat a ES6 class as a component, the @Injectable annotation annotated the ES6 Class as an Angular2 Service that is injected elsewhere.

In the above example, we’ve injected the service via providers options in the @NgModule. This way the instance of the service will be available for the entire component only and its child components, if any. However, services in Angular2 are not singleton by nature unlike Angular1 which means if the same service is injected as a provider in a child component, a new instance of the service will be created. This is a confusing thing for beginners so watch out.

The public Hello: HelloService parameter in the constructor is equivalent to Hello: HelloService = new HelloService();. It means Hello is an instance of HelloService and of a type HelloService (optional). One benefit of annotations/decorators in Angular2 in my opinion is that there is no confusion over Factory vs Service vs Provider, instead it’s just a ES6 class.

Slight changes compared to the previous example is that we need to give more configurations in SystemJS for typescript compilers to emit decorator MetaData so that generated ES5 code will work fine in a browser.

Remember experimentalDecorators flag enables experimental support for ES7 decorators in TypeScript and emitDecoratorMetadata flag emits design-type metadata for decorated declaration in ES5 output, especially, for public Hello: HelloService code in the constructor as we’d seen before. Using the alternative mentioned above will not need these flags though.

Wrap up

That’s it guys..! Wolksoftware‘s blog has covered a great intro to reflection in Typescript, if interested. In the next post, we’ll explore two-way databinding in Angular2, but meanwhile Checkout Dependency Injection in action.

Angular 2.0 is lot like Angular1 but still different in its own terms and you’ll see why as we go along. Purpose of this article is to migrate one of the simplest Angular1 examples to Angular2 and understand benefits as well as pain-points. For the record, Angular2 aimed to build web applications in three different languages or flavours i.e. JavaScript (ES5/ES6), Typescript(ES6+), and Dart. If you interested in other two then the 5-minute-session will give you a head-start to understand how it could be done. However, I’m going to use Typescript over JavaScript here because in my opinion it feels more natural. This article is for the ones who worked with Angular1 before.

Angular1

Let’s take a simple example (HTML and JS) from my free e-book on Angular1 Directives that explores how data binding works in Angular1. Let us quickly take a look at our good old Angular1 HTML template and then we’ll move to new shiny Angular2 version of it. But for now, notice we’ve used ngBind directive over double-curly notation for data-binding, obviously to avoid FOUC as we all know. Also checkout ngApp directive which was a recommended way to bootstrap an application automatically in Angular1 without using angular.bootstrap method.

Your first reaction would be, “Alright, that looks familiar..!”. Well it is except few things, let us go over one by one. But before that we must know that Angular2 moved from a concept of directives to components to leverage web-components specs so that developers can use Polymer components with Angular2 templates. Basic idea is to break down monolithic application into small pieces i.e. components and plug them together at the end under main component like we have here. Each component should have one or more Classes or Functions to store data (name in this case) and necessary methods (not defined in the example above). Please note we no longer use $scope in Angular2 as this is somewhat like CtrlAs syntax from Angular1. When Angular2 instantiates MyApp class, all properties or methods defined will be accessible via keyword this.

Update: As per RC5 release, angular2 introduced a concept of NgModule metadata which plays an important role in the compilation process, especially offline compilation. Because of NgModule, Angular2 will able to lazy load components on demand by resolving component dependencies efficiently. So every component should expose a NgModule for other components to import and reuse. Ideally, NgModule should be extracted into it’s own file importing various components, services, pipes, etc. but for the sake of readability, we’ll have it in the same file along with the component.

export statement

Angular2 has adopted modularity at its core unlike Angular1 wherein you could only define modules without any built-in support for lazy loading. Using ES6 export module syntax, you can export functions, objects, or primitives that other classes can use in Angular2. Having one export class per module recommended though. We’ve defined a property, name with a type string which is optional in TypeScript.

Import Statement

With the same export class syntax, Angular2 has organized its code base so that developers can import what they need in a module. In this example, we are only importing Component and NgModule annotations from angular2/core library and platformBrowserDynamic method from angular/platform-browser-dynamic modules. Note that the extension is optional in the definition.

Using platformBrowserDynamic().bootstrapModule method from angular2 browser module (similar to angular.bootstrap in Angular1), we can bootstrap the NgModule named MyAppModule. Angular2 is a lot different from Angular1 on the architectural level. Angular1 only targeted Desktop and Mobile web browsers, but Angular2 is platform agnostic, that means it can be used to write Native mobile apps using NativeScript or Cordova, run angular2 application inside web workers, and to enable server-side rendering with NodeJS or so. For now, we’ll just run it in a web browser by pulling down browser specific bootstrap method as above.

Annotation

The strange-looking syntax above the class called as a Class Decorator that annotates and modifies classes and properties at design time. Wolksoftware’s engineering blog has great articles on decorators and metadata in Typescript. In a nutshell, Angular2 uses decorators/annotations to make dependency injection possible. To simplify it, let us take a small requirement.

Imagine you want to log a function name and passed arguments to browser console every time a method invoked without modifying the function body. In the following example, @debug is a method decorator that attached a special behavior to the method body. overtime a method called, the decorator will find a method name being called and it’s parameter that we can log. Here is a working demo if interested.

On the same note, @component annotation/decorator tells Angular2 that the defined class, MyApp is an Angular2 Component not just a ES6 class. And once it’s defined as the component, Angular2 needs to know how the component supposed to be consumed in HTML or which template to render once it’s registered. That’s why we need to pass the meta data as above such as selector, template, etc.

Notice selector name need not be the same as the class name unlike Angular1. There is no restrict option anymore, instead use a tag name (ng-app) or a property name (with square brackets [ng-app]) or a class name (.ng-app) directly as a selector (I think a comment selector is dropped..!). Also note that we have used a double curly notation for data binding here as there is no ngBind directive available, but you can use property binding (which we’ll explore in future posts) to get the same feeling with <span>Hello, <span [textContent]="name"></span></span>.

If you remember, we’d included just angular.js in Angular1 template before, however, Angular2 relies on couple of other JavaScript libraries that you need to inject along with it. But things may change eventually, as it’s just a RC release (at the time of writing this article, and who knows we have to just include one file as before).

Refer SystemJS Wiki for more details to suite your needs. And as you guessed already, we have created a custom element in the body at the end to kick it off.

Wrap up

Peek at a demo..!. That’s it guys..! This is the exact flow you’ll always be using to write new components in Angular2. I liked the progress with Angular2 and Typescript, I would recommend to use Visual Studio Code Editor over SublimeText to feel at home. Be hopeful that many of the things we explored would be simplified by the time it reaches 1.0 (stable), I mean 2.0 😉